Wide belt sanders utilizing stationary platens are known in the prior art, with two such systems being disclosed in U.S. Pat. No. 4,651,474 to David and U.S. Pat. No. 4,864,775 to David, assigned to the same assignee as the present invention. Additionally, there have been systems developed in the past that provide oscillating movement to the entire abrasive belt or sanding head. Examples of such devices are found in U.S. Pat. No. 2,926,465 to Sommers; U.S. Pat. No. 3,094,815 to Pendergast; and U.S. Pat. No. 4,742,650 to Sauder, Jr. et al.
In a typical wide-belt abrasive finishing machine, one or more heads may be provided. The finishing head typically includes a platen interposed between a pair of rollers or drums. One or more of the drums is power driven, with the balance normally being idlers. The platen is normally interposed between a pair of horizontally aligned belt guiding rollers rotatably mounted upon parallelly disposed axes. The work passes beneath the platen and is pressed into contact with the abrasive belt while moving beneath the surface of the platen.
Typically, work is fed into the machine by a feed system or conveyor assembly that comprises an endless horizontally-oriented conveyor belt having one or more abrasive heads disposed in opposed relationship to the belt. The upper span or flight of the belt cooperates with pinch rolls so as to grip the work and feed it through the machine at a uniform rate. The top surface of the work contacts one or more moving abrasive belts during this operation. The conveyor assembly is adjustable either upwardly or downwardly toward or away from the abrasive belt assembly, in order to accommodate and adapt the apparatus to workpieces having different thicknesses. U.S. Pat. No. 3,832,808 discloses a wide belt sanding apparatus with adjustable conveyors and reference is made to this disclosure in that patent for the details of the conveyor design.
Previous abrasive finishing devices have provided oscillatory movement to the entire belt and platen system. Such systems typically have involved the oscillatory movement of the entire sanding head and entire belt supporting means including laterally disposed idlers such as in U.S. Pat. No. 4,651,474. Additionally, the tracking systems for the belts have included means for controllably maintaining the belt within a carefully delineated or controlled tracking zone. However, none of these prior abrasive finishing machines have provided controlled oscillatory movement to the platen as the belt moves across its surface.
Another attempt to improve the quality of abrasive finishing devices or machines has been to increase the width of the platen. However, such efforts have not reduced the problem of grooving or streaking of the belt contacting surface, hence the present invention finds application in connection with platens of a variety of widths.